A vehicular drivetrain

Abstract: The present invention relates to a vehicle drivetrain. The drivetrain includes an input shaft means (11,12) and a fluid torque converter (30) having a cover (21), an impeller (25) and a turbine (26). A starter ring gear (35) is secured to the cover to be engaged by a starter pinion. A coupling (14) having first and second inertia masses (16,18) operatively connects the input shaft means to the cover of the torque converter. An input isolator (20) is disposed between the first and second inertia masses for permitting relative movement therebetween. A cranking clutch (10) includes a driveplate (38) and a Belleville spring (36), the Belleville spring biasing the driveplate against the cover and reducing the likelihood of the starter pinion disengaging prematurely from the starter ring gear during the engine start procedure.

Description: The present invention relates generally to vehicular drivetrains. In drivetrain systems where the coupling between an engine and a torque converter is divided into two inertia masses, one connected with the engine and impeller and the other connected to the input shell or cover of the torque converter, an input isolator assembly is generally employed to transmit power between the inertia masses while damping torsional vibrations. The input isolators typically include a spring means. Current automatic transmissions for vehicles typically employ not only a selectively engageable friction clutch but also an isolator assembly to connect the torque converter impeller and the torque converter turbine, thereby improving the efficiency of the drivetrain. One difficulty with such systems is that engaging the clutch at low engine speeds sometimes results in vibrations in the drivetrain which are perceptible by the driver. The engagement speed range for such arrangements is, therefore, limited. Drivetrain designers have attempted to lower the engine speed at which the clutch can be engaged without generating the undesirable vibrational disturbances. Some designs have incorporated a viscous slipping clutch which is disposed in series with a friction clutch. This arrangement has the benefit of permitting lower engagement speeds, but it does increase the cost of the system. Other designers have suggested dual mass flywheel systems to reduce drivetrain disturbances in countershaft type transmissions with synchroniser shifting controls. In such designs, the engine and transmission are completely disconnected during the ratio interchanges by a selectively engageable clutch member. These systems provide some improved drivetrain damping, but they increase the number of spring systems or friction interface connections, thus becoming relatively complex and concomitantly more costly. One pertinent arrangement is disclosed in US Patent No 5,121,821. US Patent No 5,121,821 is directed to a drivetrain coupling between the engine and the torque converter that permits the friction clutch to be fully engaged at lower engine speeds, while avoiding unpleasant disturbances in the drivetrain. To accomplish this goal, the inertia mass of the torque converter, torque converter cover and clutch is separated from the engine inertia mass and, along with a portion of the flywheel inertia, is added to the transmission inertia mass. By separating these inertias, the natural frequency of the system can be designed to a lower value, thereby permitting engagement of the clutch at lower engine speeds. Moreover, the isolator can be removed from the clutch for placement between the inertia masses. This design has been effective and generally accomplishes its intended goal. The present invention contemplates a further improvement over the device as described in the aforesaid US Patent No 5,121,821. It is, therefore, a primary object of the present invention to provide a drivetrain which includes a clutch assembly selectively to bypass the input isolator. DE-A-4211840 discloses a drivetrain in accordance with the preamble of claim 1. A vehicular drivetrain in accordance with the present invention is characterised over DE-A-4211840 by the features specified in the characterising portion of claim 1. The present invention may also provide a drivetrain wherein a coupling assembly is divided into two inertia masses drivingly interconnected by a spring and friction isolator; and where in one inertia mass is rotationally coupled with the engine and impeller, and the other inertia mass is rotationally coupled with the cover of a torque converter, the cranking clutch comprising a driveplate and biasing means to urge the driveplate against the torque converter cover in order to maintain an operative connection between a starter pinion and the engine to connect the inertia masses during the engine start procedure; and wherein a biasing means urges a driveplate against the torque converter cover to bypass the isolator prior to initiation of the engine start procedure; and wherein a friction surface is biased by a Belleville spring to provide frictional contact between a driveplate and the torque converter cover; and which incorporates means for disengaging the cranking clutch assembly upon the starting of the engine. A drivetrain according to the present invention utilises a clutch in combination with a fluid torque converter that incorporates an input isolator means. The fluid torque converter has a cover, an impeller and a turbine. A coupling interconnects the crankshaft with the cover of the torque converter, and the coupling has first and second inertia masses. The first inertia mass is continuously rotatable with the engine, and the second inertia mass is continuously rotatable with the cover. The isolator means is disposed between the first and second inertia masses and permits relative movement therebetween. The clutch includes a driveplate and biasing means to bias the driveplate against the torque converter cover. The biasing means is preferably a Belleville spring. The present invention will now be described, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a cross-sectional elevation of a portion of a vehicle drivetrain in accordance with the present invention, the cranking clutch being engaged; Figure 2 is an enlarged view of that portion of Figure 1 depicting not only the driveplate utilised by the cranking clutch assembly but also the associated components of a crankshaft extension and a torque converter; Figure 3 is a cross-sectional elevational view similar to Figure 1 but depicting the cranking clutch disengaged; and, Figure 4 is an enlarged area similar to Figure 2, but depicting the cranking clutch disengaged, as represented in Figure 3. One representative form of a clutch assembly is designated generally by the numeral 10 on the accompanying drawings. With particular reference to Figures 1 and 2, an engine crankshaft 11 is secured to a crankshaft extension 12, as by a bolt 13. A coupling 14 is, in turn, secured to the crankshaft extension 12 by a second bolt 15. The coupling 14 includes an engine inertia mass 16, a two-piece housing or transmission inertia mass 18, and a plurality of isolator spring means 20. The isolator spring means 20 are disposed between the transmission inertia mass 18 and the engine inertia mass 16 in a conventional manner. The isolator spring means 20 will permit limited relative annular excursion between the engine inertia mass 16 and the transmission inertia mass 18 in order to provide isolation between the torsional disturbances of the engine and the inertia masses 16 and 18. The transmission inertia mass 18 is secured to a torque converter cover 21 which is rotatably supported on bushings 27 and 29. The crankshaft extension 12 is supported through a bushing 22 on a sleeve 23 which is secured to a stationary housing. The cover 21 is drivingly connected to a torque converter impeller 25 through isolator spring means 20. The impeller 25 is disposed in toroidal flow relationship with a torque converter turbine 26 and a torque converter stator 28. The impeller, turbine and stator cooperate to form a conventional torque converter 30, the operation of which is sufficiently well known such that a further description of its structure and operation is not deemed to be necessary. The torque converter 30 will permit slippage between the engine input and the turbine output which effectively dampens torsional vibrations and permits torque multiplication during the converter phase. As such, a torque converter will permit smooth vehicle acceleration and deceleration, while allowing the engine to operate at the most appropriate torque output level. These are the primary purposes for using a torque converter. The primary drawback of a torque converter is, of course, that during the coupling phase, slippage between the impeller and the turbine constitutes an efficiency loss and therefore adversely affects fuel economy. In order to improve the fuel economy, a torque converter override clutch plate 31 is disposed between the turbine 26, and the cover 21. When a friction disk 32 on a radially outer portion 33 of the torque converter clutch plate 31 engages the cover 21, the torsional vibrations present at the engine crankshaft 11, such as those caused by the firing frequency of the engine cylinders, can be transmitted to the torque converter output 34. The isolator spring means 20 are operable to effect a significant reduction or elimination of the transmission of transient torque spikes that might otherwise be imposed on the torque converter output 34. As depicted, the isolator spring means 20 separate the engine inertia mass 16 from the transmission inertia mass 18. By astute separation of these inertia masses, the natural frequency of the system can be reduced to a lower value, thereby permitting engagement of the override clutch plate 31 at lower engine speeds. The interstices between the components of that portion of the drivetrain depicted result in the free flow of hydraulic fluid therethrough, such that the fluid can accomplish cooling and lubrication of the various coupling components. As will be hereinafter more fully explained, the flow of hydraulic fluid through the interstices will assist in the operation of the cranking clutch 10. In order to prevent the fluid from leaking to atmosphere, some applications employ a bladder (not shown) that encapsulates the interior of the torque converter 30. It has been determined that the addition of the cranking clutch assembly 10 can improve performance when starting the engine. With reference to FIGS. 1-4, when a torque converter 30 is coupled to an engine crankshaft through an input isolator 20, it is often desirable to attach a starter ring gear 35 to the cover 21. However, this location of the starter ring gear 35 can be inconvenient when cranking the engine during the starting procedure. Because the cranking torque must be transmitted through the isolator spring means 20, the relatively low torsional rate of the input isolator spring means can allow the system to oscillate with a high amplitude and prematurely disengage the starter pinion (not shown) from the starter ring gear 35. This potential problem can be reduced or eliminated by using the cranking clutch assembly 10 such as shown in Figures 1-4. The cranking clutch assembly 10 comprises a biasing means 36 and a driveplate 38. In a preferred embodiment, the biasing means 36 may be a Belleville spring that is mounted on the shaft extension 12 by a retaining ring 39 received within an annular recess 40 provided in the radially outer surface of the shaft extension 12. The driveplate 38 is tanged or splined to the crankshaft extension 12 and includes friction material 41 on the radially outwardly disposed portion of that surface 42 of the driveplate 38 which faces the cover 21. The biasing force applied by the Belleville spring 36 as it engages the driveplate 38 urges the friction material 41 on the driveplate 38 into engagement with the cover 21 so that cranking torque can be transmitted from the starter ring gear 35 to the crankshaft extension 12 while bypassing the isolator spring means 20. Once the engine has started, however, the pressure of the hydraulic fluid which charges the torque converter forces the hydraulic fluid through the interstices and against the driveplate 38 to disengage the cranking clutch assembly 10. This enables the input isolator spring means 20 to function as intended. Typically, the interstices between the various components of the torque converter 30 and the associated assembly -- as indicated by the shade lines in Figure 4 -- are sufficient to effect the desired timing to the actuation of the cranking clutch assembly 10, but if desired, a passageway (not shown) may be provided between a main torque converter cavity 43 and a cranking clutch deactivating cavity 44 -- that is bounded on one side by surface 42 on the driveplate 38 -- can be provided to effect a desired timing for the disengagement of the cranking clutch assembly 10. In order to assure the integrity of the cranking clutch deactivating cavity 44, an annular recess 45 may be recessed within a hub portion 46 of the driveplate 38 to receive a sealing means 48, such as the O-ring depicted, that will sealingly engage a cylindrical outer surface 49 of the shaft extension 12. It should be appreciated that a plurality of such passageways may be provided in the structure depicted in order to facilitate access of the fluid serving to cool and to lubricate the structure. The cranking clutch assembly 10 provides a positive drive to rotate the engine crankshaft 11 when the starter motor is rotated, while bypassing the isolator spring means 20.

Claims: A vehicular drivetrain comprising output shaft means (12) of the crankshaft (11) of the engine of the vehicle which output shaft means forms input shaft means (12) of the drivetrain; a fluid torque converter (30) having a cover (21), and impeller (25) and a turbine (26); a coupling (14) having isolator means (20) and first and second inertia masses (16,18), the first inertia mass (16) being continuously rotatable with the input shaft means (12), and the second inertia mass (18) being continuously rotatable with the cover (21); the isolator means (20) being disposed between the first and second inertia masses (16,18) for permitting relative movement therebetween; and a clutch assembly (10) having biasing means (36); characterised in that the coupling (14) interconnects the input shaft means (12) and impeller (25) with the cover (21); and that an axially movable driveplate (38) carried on and continuously rotatable with the input shaft means (12) is biased by the biasing means (36) into driving engagement with the cover (21) during selected phases in the operation of the input shaft means. A vehicular drivetrain as set forth in Claim 1, wherein the biasing means is a spring (36). A vehicular drivetrain as set forth in Claim 2, wherein the spring is a Belleville spring (36). A vehicular drivetrain, as set forth in any one of Claims 1 to 3, wherein the driveplate (38) further comprises a surface (42) facing the cover (21); a friction means (41) secured to the surface for providing driving contact between the driveplate and the cover. A vehicular drivetrain as set forth in Claim 4, wherein the driveplate (38) has a radially outer portion; and the friction means (41) is affixed to the radially outer portion. A vehicular drivetrain as set forth in any one of Claims 1 to 5, further comprising means for disengaging the clutch assembly (10) upon starting of an engine driving the input shaft means (12). A vehicular drivetrain as set forth in Claim 6, wherein the disengaging means comprises pressurised fluid from the torque converter (30). A vehicular drivetrain as set forth in Claim 7, wherein a pressure chamber (43) is provided in the torque converter (30) ; and passage means are provided between the pressure chamber in the torque converter and the driveplate (38); the pressurised fluid flowing through the passage means. A vehicular drivetrain as set forth in Claim 8, wherein the size of the passage means is selected to adjust the timing of the disengagement of the clutch assembly (10).

Inventors: VAN MAANEN KEITH D, VAN MAANEN, KEITH D.
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1994
Main classification: F16F15
IPC codes: F16F15, F16H45, F16H41